The effectiveness of a variety of therapeutic procedures, including the use of pharmaceuticals, chemotherapy, and gene therapy, depends in large part on the ability to deliver bioactive compounds into target cells. Such bioactive compounds include, but are not limited to, proteins, nucleic acids, protein-nucleic acid fusion molecules, polysaccharides, metals, metal ions, and synthetic organic molecules.
Because the efficacy of a variety of therapeutic procedures derives in large part from the ability to deliver bioactive compounds into target cells, the delivery of bioactive compounds into non-targeted cells can have grave consequences for the patient being treated. Specifically, delivery of bioactive compounds into non-targeted cells can create a multitude of side effects which may outweigh any benefits realized from the application of the therapeutic procedure. Furthermore, for a finite amount of a bioactive compound, the effective concentration of the bioactive compound in target cells is reduced as a result of delivering the bioactive compound into non-targeted cells.
Two conventional methods for delivering bioactive compounds into target cells illustrate the difficulty surrounding the delivery of genetic material into target cells without the concomitant introduction of genetic material into non-targeted cells. Viral vectors and liposomes can be utilized as a means of delivering therapeutic genetic material into target cells. Ordinarily, the viral vectors and/or liposomes are injected directly into the bloodstream of the patient or are combined ex vivo with cells which are removed from the patient and which are subsequently returned to the patient upon being genetically altered. See generally, Scientific American, June 1997, pp. 96-120. However, both of the foregoing mechanisms result in delivery of genetic material into non-targeted cells. Injection into the bloodstream allows the viral vectors to infect and the liposomes to fuse with non-targeted cells because the viral vectors and/or liposomes are dispersed throughout the patient's body. Similarly, in the absence of a method by which target cells can be isolated from a mixture of target and non-target cells, the ex vivo combination of viral vectors and/or liposomes with cells removed from the patient also will result in delivery of genetic material into non-targeted cells. Therefore, the value of the above delivery methods is limited to the extent that both methods lead to the introduction of genetic material into non-targeted cells and, consequently, attenuate the effectiveness of the underlying therapeutic procedure.
In view of the foregoing problems, there exists a need for a method by which bioactive compounds can be delivered into cells in a site-specific fashion. The present invention provides for such a delivery method and associated compositions useful therefor. These and other advantages of the present invention, as well as additional inventive features, will be apparent from the description of the invention provided herein.